Photoproduction of meson and baryon resonances in a chiral unitary approach

By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.Comment: Contribution to the Erice Summer School of Nuclear Physics, 21th course: Electromagnetic Probes and the Structure of Hadrons and Nuclei September 17th - 25th, 1999, Erice/Sicily/Ital

Recent progress on the chiral unitary approach to meson meson and meson baryon interactions

We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and $K^-$ atoms.Comment: Contribution to the KEK Tanashi Symposium on Physics of Hadrons and Nuclei, Tokyo, December 1998, 10 pages, 3 postscript figures. To be published as a special issue of Nuclear Physics

Numerical modelling of the cyclic structural behavior of slender steel members with restrained buckling

Este trabajo presenta un modelo numérico del comportamiento estructural cíclico de barras de pandeo restringido, comúnmente utilizadas como una alternativa a las clásicas barras de arriostramiento concéntrico para protección sismorresistente de pórticos de edificios y otras estructuras. Estos dispositivos se componen normalmente de un núcleo de acero esbelto recubierto por una carcasa de mayor rigidez que tiene por objeto impedir su pandeo cuando se encuentra comprimido. La carcasa puede ser de mortero o de acero, y una interfaz de deslizamiento está interpuesta entre el núcleo y la carcasa para evitar la transferencia excesiva de tensiones tangenciales. El comportamiento del núcleo de acero se describe mediante un modelo de daño y plasticidad, el comportamiento de la carcasa de mortero se describe mediante un modelo de daño isótropo y el comportamiento de la interfaz de deslizamiento se describe mediante un modelo de penalización de contacto. Estos 3 modelos se implementan en el paquete de software Abaqus siguiendo una formulación explícita. En un artículo previo publicado en una revista de ingeniería sísmica se describió someramente el modelo, se comprobó de forma preliminar su capacidad para reproducir el comportamiento cíclico de barras de pandeo restringido y se compararon satisfactoriamente sus resultados con los de ensayos experimentales; el objetivo de este trabajo es describir el modelo en profundidad y discutir en mayor extensión las valoraciones acerca de su utilidad.This work presents a numerical model of the cyclic structural behavior of dissipative buckling-restrained braces, commonly used as an alternative to classical concentric braces for seismic protection of building frames and other structures. Such devices are usually composed of a slender steel core embedded in a stockiest casing that is intended to prevent its buckling when it is under compression. The casing is made either of mortar or steel, and a sliding interface is interposed between the core and the casing to prevent excessive shear stress transfer. The behavior of the steel core is described by a damage and plasticity model; the behavior of the mortar casing is described by an isotropic damage model and the sliding behavior of the interface is described by a contact penalty model. These 3 models are implemented in the Abaqus software package following an explicit formulation. In a previous article (published in an earthquake engineering journal) the model was briefly described, its ability to reproduce the cyclical behavior of buckling-restrained braces was preliminarily pointed out and their results were satisfactorily compared with those of experimental tests. The aim of this paper is to describe the model thoroughly and to present new judgments about its usefulness.Peer Reviewe

Chiral Unitary Approach To The N*N*pi, N*N*eta Couplings For The N*(1535) Resonance

Using a chiral unitary model in which the negative parity nucleon resonance $N^\ast \equiv N^\ast(1535)$ is generated dynamically by means of the Bethe Salpeter equation with coupled meson baryon channels in the $S = 0$ sector, we have obtained the $\pi^0 N^\ast N^\ast$ and $\eta N^\ast N^\ast$ couplings. The $\pi^0 N^\ast N^\ast$ coupling has smaller strength and the same sign as the $\pi^0 N N$ coupling. This rules out the mirror assignment of chiral symmetry where the ground state nucleon $N$ and the negative parity resonance $N^\ast$ are envisaged as chiral partners in the baryon sector.Comment: 30 pages, 15 figures (ps files). The new version discusses pi-N scattering around the N*(1535) resonanc

Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector

We study the S-wave interaction of mesons with baryons in the strangeness S=0 sector in a coupled channel unitary approach. The basic dynamics is drawn from the lowest order meson baryon chiral Lagrangians. Small modifications inspired by models with explicit vector meson exchange in the t-channel are also considered. In addition the pi pi N channel is included and shown to have an important repercussion in the results, particularly in the isospin 3/2 sector.Comment: 23 pages, LaTeX, 21 figure

Modelización numérica del comportamiento estructural de barras de pandeo restringido

Los disipadores de energía son elementos pasivos que se incorporan a edificios y a otras construcciones que, pueden estar sometidas a acciones dinámicas, especialmente movimientos sísmicos. Su finalidad es absorber la mayor parte de la energía introducida en la estructura por la excitación, protegiendo de esta manera la estructura principal. Estos dispositivos son relativamente ajenos a la estructura, en el sentido que no participan en la resistencia a cargas verticales, y, por tanto, son fácilmente reemplazadas después de sufrir daños importantes. Se conectan a la estructura a proteger de forma que cuando ésta sufre la acción del terremoto, se generan deformaciones importantes en los disipadores produciéndose de esta manera la absorción de energía. En estructuras de edificación, los disipadores se colocan en pórticos; habitualmente en barras de arriostramiento concéntrico entre plantas, (generalmente diagonales o en V invertida) ya que, al producirse desplazamientos relativos entre plantas (“interstory drift”), aparecen deformaciones apreciables en estos elementos. Se han propuesto distintos tipos de disipadores para estructuras de edificación. Los basados en plastificación de metales, conocidos habitualmente como histeréticos, destacan por su sencillez, economía y robustez; de entre éstos las denominadas barras de pandeo restringido han conocido un notable desarrollo por poseer ventajas relevantes. Básicamente son barras concéntricas de arriostramiento, constituidas por un núcleo delgado de acero que se rodea de un revestimiento, generalmente de mortero y/o acero. Es de vital importancia que exista un interfaz, entre el núcleo y el revestimiento, que permita el deslizamiento entre ambos para evitar que parte de las estensiones del núcleo se plastifica, ya que el revestimiento impide su pandeo; estos ciclos de plastificación por tracción y compresión cosntituyen los lazos de histéresis a través de los cuales se disipa energía. A pesar de la notable experiencia, tanto a nivel de investigación como de aplicaciones prácticas, que existe sobre las barras de pandeo restringido, aún quedan numerosos interrogantes abiertos. En particular, no han sido propuesto ningún modelo numérico que simule con exactitud y fiabilidad su comportamiento estructural, ya que, éste es notablemente complejo, debido al trabo conjunto y multiaxial de distintos materiales (acero del núcleo,mortero y acero del revestimiento). Esta ausencia impide comprender a fondo los fenómenos complejos que suceden durante la operación de estos elementos, y dificulta el desarrollo de soluciones innovadora, ya que no es posible conocer con exactitud su comportamiento de barras de pandeo restringido formadas por un núcleo de acero, un interfaz deslizante y un revestimiento de mortero eventualmente rodeado por una funda exterior de acero. En el modelo numérico propuesto, el acero tiene un comportamiento elastoplástico con endurecimiento cinemático isótropo. Para el mortero que le rodea se han desarrollado u modelo isótropo de daño. La parte de acero del revestimiento (funda) se homogeneiza al mortero. La interfaz entre el núcleo de acero puede penetrar en el mortero. En el presente trabajo, estos modelos se implementan en subrutinas del programa Abaqus/Explicit, permitiendo comprobar el funcionamiento del modelo que se propone. Los resultados obtenidos, con este modelo numérico, se compararon con los resultados experimentales obtenidos en la Universidad de Girona y en la Universidad de California

Electron-scattering cross sections for collisions with tetrahydrofuran from 50 to 5000 eV

In this paper, we report on total electron tetrahydrofuran (C4 H8 O) scattering cross-section measurements for energies in the range from 50 to 5000 eV with experimental errors of about 5%. In addition, integral elastic and inelastic cross sections have been calculated over a broad energy range (1-10000 eV), with an optical potential method assuming a screening-corrected independent atom representation. Partial and total ionization cross sections have been also obtained by combining simultaneous electron and ion measurements with a time-of-flight analysis of the ionic induced fragmentation. Finally, an average energy distribution of secondary electrons has been derived from these measurements in order to provide data for modeling electron-induced damage in biomolecular systems. © 2009 The American Physical Society.de Educación y Ciencia Plan Nacional de Física, This study has been partially supported by the following research projects and institutions: Ministerio Project No. FIS2006-00702, Consejo de Seguridad Nuclear CSN, European Science Foundation COST Action CM0601 and EIPAM Project, Acciones Integradas Hispano-Portuguesas Project No. HP2006-0042Peer Reviewe

Chiral dynamics of p-wave in K^- p and coupled states

We perform an evaluation of the p-wave amplitudes of meson-baryon scattering in the strangeness S=-1 sector starting from the lowest order chiral Lagrangians and introducing explicitly the Sigma^* field with couplings to the meson-baryon states obtained using SU(6) symmetry. The N/D method of unitarization is used, equivalent, in practice, to the use of the Bethe-Salpeter equation with a cut-off. The procedure leaves no freedom for the p-waves once the s-waves are fixed and thus one obtains genuine predictions for the p-wave scattering amplitudes, which are in good agreement with experimental results for differential cross sections, as well as for the width and partial decay widths of the Sigma^*(1385).Comment: LaTeX, 18 pages, 6 figure

Measuring the Relative Strong Phase in D0→K∗+K−D^0 \to K^{*+} K^- and D0→K∗−K+D^0 \to K^{*-} K^+ Decays

In a recently suggested method for measuring the weak phase $\gamma$ in $B^\pm \to K^\pm (KK^*)_D$ decays, the relative strong phase $\delta_D$ in $D^0 \to K^{*+} K^-$ and $D^0 \to K^{*-} K^+$ decays (equivalently, in $D^0 \to K^{*+} K^-$ and \od \to K^{*+} K^-) plays a role. It is shown how a study of the Dalitz plot in $D^0 \to K^+ K^- \pi^0$ can yield information on this phase, and the size of the data sample which would give a useful measurement is estimated.Comment: 13 pages, latex, 5 figures, submitted to Phys. Rev. D. Appendix and some text on additional resonant contributions adde

Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances

We determine the helicity amplitudes A_1/2 and radiative decay widths in the transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3 \pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the ratio would, thus, provide direct access to the nature of the Lambda(1670). To compare the result for the Lambda(1670), we calculate the helicity amplitudes A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A_1/2.Comment: 15 pages, 8 figure